Maraapunisaurus fragillimus, N.G. (formerly Amphicoelias fragillimus), a basal Rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado

Abstract

In 1878, Oramel Lucas shipped to E.D. Cope of the Academy of Natural Sciences of Philadelphia, a huge 1.5-m-tall neural spine from the dorsal vertebra of a sauropod (from the Upper Jurassic Morrison Formation) that Cope named and illustrated as Amphicoelis fragillimus.The holotype was lost and all that is known of the specimen is from Cope's original publication. Reanalysis of Cope's publication in light of other sauropods discovered since 1878 indicates that Amphicoelias fragillimus is a basal rebbachisaurid characterized by pneumatic neural spine and arch, and the unambiguous rebbachisaurid character of a festooned spinodiapophyseallamina. Because the specimen can no longer be referred to the basal diplodo­ coid Amphicoelias, the genus name is replaced with Maraapunisaurus n.g. As a rebbachisaurid, revised dimensions indicate a dorsal vertebra 2.4 m tall and a head-to-tail length for the animal of 30.3 to 32m, significantly less than previous estimates.